Reason Donald C, Ullal Anuska, Liberato Justine, Sun Jinying, Keitel Wendy, Zhou Jianhui
Children's Hospital Oakland Research Institute, 5700 Martin Luther King Jr. Way, Oakland, CA 94609, USA.
Vaccine. 2008 Jul 29;26(32):4041-7. doi: 10.1016/j.vaccine.2008.05.023. Epub 2008 Jun 2.
Protective antigen (PA) is the cell surface recognition moiety of the Bacillus anthracis A-B toxin system, and the active immunogenic component in the currently licensed human anthrax vaccine (BioThrax, or AVA). The serum antibody response to the PA protein is polyclonal and complex both in terms of the antibody combining sites utilized to bind PA and the PA-associated epitopes recognized. We have cloned, sequenced, and expressed a large panel of PA-specific human monoclonal antibodies from seven AVA-immunized donors. Dot blots, Western blots, and radiolabeled antigen capture assays employing both proteolytic fragments of PA and engineered PA sub-domain fusion proteins were used to determine the region (domain) of the PA monomer to which each of the cloned human antibodies bound. The domain specificity of the isolated monoclonals was highly biased towards the amino-terminal 20kDa fragment of PA (PA(20)), with the majority (62%) of independently arising antibody clones reacting with determinants located on this PA fragment. A similar bias in domain specificity was also demonstrated in the serum response of AVA-vaccinated donors. Since PA(20) is cleaved from the remainder of the monomer rapidly following cell surface binding and has no known role in the intoxication process, the immunodominance of PA(20)-associated epitopes may directly affect the efficacy of PA-based anthrax vaccines.
保护性抗原（PA）是炭疽芽孢杆菌A-B毒素系统的细胞表面识别部分，也是目前已获许可的人用炭疽疫苗（BioThrax，或AVA）中的活性免疫原成分。针对PA蛋白的血清抗体反应在用于结合PA的抗体结合位点以及所识别的PA相关表位方面都是多克隆且复杂的。我们从7名接种AVA的供体中克隆、测序并表达了大量PA特异性人单克隆抗体。采用PA的蛋白水解片段和工程化PA亚结构域融合蛋白进行的点杂交、蛋白质印迹和放射性标记抗原捕获分析，用于确定每个克隆的人抗体所结合的PA单体区域（结构域）。分离出的单克隆抗体的结构域特异性高度偏向于PA的氨基末端20kDa片段（PA(20)），大多数（62%）独立产生的抗体克隆与位于该PA片段上的决定簇发生反应。在接种AVA的供体的血清反应中也显示出类似的结构域特异性偏向。由于PA(20)在细胞表面结合后会迅速从单体的其余部分裂解下来，并且在中毒过程中没有已知作用，PA(20)相关表位的免疫显性可能直接影响基于PA的炭疽疫苗的效力。
